JPH0454860A - Linear brushless dc motor - Google Patents

Abstract

PURPOSE:To set a thrust variation to substantially completely zero by varying a thrust of an armature coil sinusoidally with a pitch equal to a magnetizing pitch T of a field permanent magnet. CONSTITUTION:An armature coil 31 and a field permanent magnet 51 are opposed through a narrow air gap. A linear scale 4 is mounted between light emitting elements E1, E2 and photodetectors R1, R2 branched in a fork state. The scale 4 is formed of glass in a light shielding pattern to vary the quantity of light incident to the photodetectors R1, R2. The length of a part for transmitting a light is varied in accordance with the waveform of an armature coil current necessary to obtain a sinusoidal thrust by transmitted light amount. When a light transmitted in the pattern of the scale 4 is incident on the photodetectors R1, R2, the driving current of an armature coil 32 is controlled by a command from a servo controller.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multipolar DC linear motor used for positioning a robot X-Y stage or the like.

[Conventional technology]

For the basic structure of multi-pole DC linear motors and their driving methods, see, for example, "Linear Motors and Their Applications"
, Institute of Electrical Engineers of Japan, 1981, pp. 9-10. This motor is composed of a multi-pole magnetized permanent magnet and multiple coils, and generates thrust in a constant direction over a long stroke to move.The motor is designed to minimize thrust fluctuations due to position. To this end, measures have been taken to change the drive current according to changes in the relative position with respect to the magnet.

A specific example of this type of linear motor configured as a movable armature three-phase brushless motor is shown in FIG. In Fig. 6, (a) is a perspective view showing the arrangement of the stator (field permanent magnet), mover (armature coil), and magnetic pole detection Hall element, and (b) shows the relative positional relationship in more detail. FIG.

In FIG. 6, 2 is a mover substrate made of an insulator, 31
, 32.33 is the armature coil placed thereon, 41
, 42 and 43 are Hall elements for magnetic pole detection. Also, 5
0.70 is stator yoke, 51-58 is stator yoke 5
The field permanent magnets 71 to 78 are arranged on the stator yoke 70.

The stator yokes 50 and 70 are configured to sandwich the movable base plate 2, and the movable base plate 2 is attached to a linear slider (not shown) so as to be able to reciprocate in the direction of the arrow.

Since the field permanent magnets are arranged as shown in the figure, for example, an upward magnetic field H+ is applied to the part between magnets 56 and 76.
However, there is also a downward magnetic field H between the magnets 57 and 77.
- is generated, and an alternating magnetic field in the vertical direction is generated in the same way between other magnets. The repeating pitch is T, which is equal to the width of the magnet.

Next, a circuit for exciting the armature coil 31 etc. will be explained with reference to FIG. In this configuration example shown in Fig. 6,
There are three sets of armature coils and Hall elements, and three-phase drive is possible, and this circuit corresponds to one phase of them.

In the figure, 31 is an armature coil, 41 is a Hall element,
OP is an operational amplifier, T and T are output transistors. The circuits for the other two phases are similar, and the power supply +V
cc and -Vcc are shared, and command voltage E is also commonly applied.

It is now assumed that a command voltage E corresponding to a certain required thrust force and its direction is being applied. When the Hall element 31 receives a magnetic field, an output voltage proportional to the magnetic field appears, which is amplified by the operational amplifier OP, and further by the transistor T, .
A driving current flows through the armature coil 31 after being amplified by T. The magnitude and direction of this current are determined by the Hall element 4
1 is configured to be proportional to the magnitude and polarity of the output voltage. Therefore, the magnitude and direction of this current are proportional to the magnitude and direction of the command voltage E and the magnitude and direction of the magnetic field received by the Hall element 41.

Further details will be described using FIG. 6(b). When the relative positions of the mover and stator are as shown in the figure, the armature coil 31 is in a state spanning both the magnets 51.71 and 52.72. A portion 31A of the coil 31 perpendicular to the movable direction of the armature is placed in the downward magnetic field H- generated by the magnet 51.71, and a portion 31B of the armature coil is placed in the downward magnetic field H- generated by the magnet 52. It is placed in an upward magnetic field H+ generated by .72. Also,
The Hall element 41 is also placed in the upward magnetic field H+ like the armature coil portion 31B.

In this state, the direction of the current in the armature coil generated by the output of the Hall element 41 (generated by being amplified by the circuit in Figure 5) is as shown by Q and x in Figure 6(b). , command voltage E is set, both armature coil portions 31A and 31B receive a force in the right direction. This force moves the mover to the right, but T
When the armature coil parts 31A, 31B and the Hall element 41 move by /2, they all come to the area where the magnetic field of the alternating magnetic field = 0, so the Hall element output becomes zero, and therefore the drive current flowing through the armature coil also becomes zero, and this No thrust is generated at the point. When the mover moves further due to inertia, it enters the area next to the alternating magnetic field, so that the portion 31A of the armature coil
, 31B are reversed, but the magnetic field received by the Hall element 41 is also reversed, and therefore the drive current of the armature coil is also reversed. Therefore, the force received by the armature coil 31 is still to the right, and the mover is directed to the right. Continue moving to.

Looking only at the armature coil 31, its rightward force repeatedly fluctuates between the maximum value and zero.

The period of variation is the magnet width T. However, armature coils 32 and 33 are also attached to the mover, and their relative positions with respect to the magnets are phase-shifted by T/3, so that fluctuations in the total rightward thrust are averaged out. In particular, if the alternating magnetic field is configured to vary sinusoidally between Hya → 0 → H-, no fluctuation will appear in the total thrust force.

If the polarity of the command voltage is reversed, the direction of thrust will be to the left. Further, the magnitude of the thrust changes in proportion to the command voltage.

The above description has been made by taking as an example a so-called three-phase drive system in which there are three armature coils, and the relative positions of the armature coils with respect to the magnets are shifted by T/3. If N armature coils are provided and their relative positions with respect to the magnets are shifted by T/N, this becomes what is called an N-phase drive system.
As N becomes larger than 3, the thrust becomes more averaged, and especially if the alternating magnetic field by the field magnet is configured to vary in a sinusoidal manner, no thrust fluctuation will appear at all.

[Problem 1 to be Solved by the Invention Above is a specific example of the configuration of a multi-phase drive type linear brushless motor. This method can provide excellent characteristics with extremely small thrust fluctuations if the distribution of the alternating magnetic field produced by the field permanent magnet can be brought close to a sine wave.

However, making the distribution closer to a sine wave also has negative effects. Although it is possible to approximate this by optimizing the shape, size, arrangement, etc. of the field permanent magnets, this results in an increase in the processing cost of the magnetic circuit and a decrease in the efficiency of magnet use.

Furthermore, even if the distribution of the alternating magnetic field is close to a trapezoidal wave,
By increasing the number of phases, it is possible to reduce thrust fluctuations.

However, in order to increase the number of phases, it is necessary to increase the number of armature coils, which leads to an increase in cost.

[Means for solving problems]

The inventors solved the problem by using a light receiving/emitting element instead of the Hall element for magnetic pole detection and combining this with an optical linear scale having a pattern corresponding to the magnetic field of the field permanent magnet.

The first purpose of having such a configuration is that when the movable element moves, the period of thrust by one armature coil is equal to the magnetization pitch T of the field permanent magnet. The purpose is to make the change occur in a sinusoidal manner. By using two or more such armature coils in a multiphase arrangement, thrust fluctuations can be made almost completely zero.

Another objective is that by using light receiving and emitting elements instead of Hall elements, position information is not affected by magnetic fields, making the overall configuration of the linear motor easier, and improving safety against temperature changes. A-ru.

Prior to describing embodiments, the basic idea of the present invention will be described below.

FIG. 8 is a diagram showing the principle configuration of a moving armature linear motor focusing on only one armature coil.

In the figure, l is a field permanent magnet that is alternately magnetized with multiple poles at a pitch T, 2 is a mover configured to be movable in the longitudinal direction (arrow direction) of the field permanent magnet 1, and 3 is a movable member. Child 2
This is an armature coil with an opening angle T disposed above the .

In the figure, the thrust force acting on the coil 3 is F = K N i B (1). Here, K is a constant, N is the number of turns of the coil, i is the current flowing through the coil, and B is the magnetic flux density of the part where the coil is placed. (Since the opening angle T of the coil and the magnetization pitch T are configured to be equal, the magnetic flux density in the part where one side In of the coil is placed and the magnetic flux density in the part where the other side ■■ is placed are The direction is opposite but the magnitude is equal, and both are B. Also, the current flowing through one side III of the coil and the current flowing through the other side mlV are opposite in direction but equal in magnitude, and both are i. Therefore, the thrust force is expressed as above.) By the way, when the thrust force F changes in a sinusoidal manner with a period T as the armature 3 moves, if this coil has a multiphase configuration, the thrust fluctuations can be suppressed. It is somewhat difficult to show in general that it can be zero, but if the phase number is 2, 3, etc. ...It is easy to decide quickly and calculate this time. Here, just to be sure, examples will be shown for two-phase excitation and three-phase excitation.

In the configuration example shown in FIG. 8, the fact that the thrust of one coil is sinusoidal means that the thrust F changes in the following manner. That is, 2π F=' (1-cos -X) (2) where ' is a constant. When X changes, F changes sinusoidally with period T between a minimum value of zero and a maximum value of 2'.

First, the case of two-phase excitation will be described. Two coils, T
The resultant thrust when they are spaced apart by /2 is T.

Then, 2π T, = to' [(1-cos −・X) Calculating this using the addition theorem of ten trigonometric functions, we get T, = 2''
(3) becomes.

It can be seen that the thrust T is a constant that does not include the term X, and no thrust fluctuation occurs.

In the case of three-phase drive excitation, the three coils are connected to T.
If the combined thrust when they are spaced apart by /3 is T, then 2π T3 =' [(1-cos ・X) 10 = 3' (4) In other words, no thrust fluctuation occurs. In the case of four or more phases, it is obtained in the same way.

By the way, as a means to make the thrust force acting on the coil 3 expressed by equation (1) into a form like equation (2), it may be done as follows. From (1) and (2), F-KN i
B = ni' (1-cos-X) 22, K, ni', and N are constants, and B is the magnetic flux distribution due to the field permanent magnet, which is a function of X, but by some means It is only necessary to control i so that it satisfies the relationship of equation (5). What kind of pattern shape does equation (5) represent?
In order to clarify this point, we performed the following calculations.

FIG. 9 is an example of actual measurement of magnetic flux distribution by a field permanent magnet.

This was modeled by making it dimensionless into a pattern as shown in Figure 1O(a).

Next, FIG. 10(b) shows the ideal thrust waveform shown by equation (2) dimensionless by one wavelength.As shown by equation (5), FIG. The function representing the waveform in (b) divided by the function representing the waveform in Figure 10 (a) (when X is a certain value, the corresponding value of F is divided by the value of B, i ) is a function indicating the waveform required for i. FIG. 10(C) shows the results of this calculation.

As can be seen from the figure, although it is a pseudo sine wave, there are discontinuous points in the slope, and it is not necessarily easy to obtain such a signal using a magnet and a Hall element.

The inventors came up with the idea of using a combination of a light receiving/emitting element and a linear scale as a means for obtaining such a signal regarding position.

〔Example〕

This will be explained below using examples.

(Embodiment 1) FIG. 1 is a perspective view showing the constituent parts of an embodiment of the present invention, and FIG. 2 is a side view showing the relationship between the components of this embodiment in an assembled state.

In FIG. 1, 1 is a stator base, 2 is a mover board, 31
32 is an armature coil arranged downward on the mover board, 4 is a linear scale, 50 is a stator yoke made of soft magnetic material, and 51 to 58 are arranged above the stator yoke. 61 is a light receiving/emitting element case for determining the drive current to be passed through the armature coil 31; 62 is a light receiving/emitting element case for determining the drive current to be passed through the coil 32;

In Figure 1, the stator and mover are shown separated to make it easier to see the parts that make up the stator and mover, but in reality, the field permanent magnets on the stator and the armature coil on the mover side are The movable element faces the field permanent magnet in the longitudinal direction (
It is supported by a bearing mechanism (not shown) so that it can move along the direction of the arrow. Furthermore, in the assembled state, the linear scale 4 is arranged so as to be sandwiched between the light receiving and emitting element cases 61 and 62.

FIG. 2 shows a side sectional view of that of FIG. That is,
When the mover is in the assembled state, the mover is at the end position of the stator (the left end in FIG. 1), and the armature coil 31 and the field permanent magnet 51 are facing each other, a cross-sectional view at this position is shown. . The armature coil 31 and the field permanent magnet 51 face each other with a narrow gap in between (the same applies to other armature coils and field permanent magnets), and the linear scale 4 is branched into a scissor shape. It is located between the light receiving and emitting element cases. In the figure, E and E are light emitting elements, and R and R are light receiving elements.

In this example, we start with E, E, and then replace the LEDs with R,...
A photodiode is used as R. The light emitted from E is detected by R1, and the light emitted from R2 is detected by R1. The linear scale is made of glass, and a light-shielding pattern as described later is formed in the portions 41A and 41B to change the amount of light incident on the photodiode R3°R2.

FIG. 3 is a diagram showing a light shielding pattern of the linear scale 4 in this embodiment. In the figure, one-dot chain line 41A, 4
What is indicated by 1B is a two-channel light-shielding pattern section, in which the hatched portion is a portion that blocks light, and the white portion is a portion through which light is transmitted.

41A corresponds to a portion where the surface of the field permanent magnets 51 to 58 (the surface facing the armature coil) is the north pole, and 42A corresponds to a portion where the surface is the south pole. For each channel, the length of the part that transmits light is T,
The amount of transmitted light changes in accordance with the waveform of the armature coil current necessary to obtain a sinusoidal thrust as shown in FIG. 10(c).

FIG. 4 is a diagram showing a drive circuit that generates an armature coil drive current having a predetermined pattern using the linear scale and light receiving/emitting elements. In the figure, E, E are LEDs arranged in the light receiving/emitting element case 61, R,...
R, is a photodiode arranged in the light receiving/emitting element case 61, OP, ~OP are operational amplifiers, and IC, is a double-pole double-throw (DPD) that switches the circuit according to an external command voltage.
T) is an electronic switch, T,', T is a current amplification transistor, and 31 is an armature coil. E,, E,
The light emitted from each path R
I Inject into IR8. At this time, the emitted light has an intensity proportional to the magnitude of the command voltage E from the servo control circuit.
6 The transmitted light is blocked by 1B according to a preset pattern.

Or, when it enters R8, a current proportional to the amount of incident light flows through R or R3, and this flows into OP or OF.
, and after selecting the polarity corresponding to the command voltage E' by the electronic switch IC3, it is linearly amplified by the transistor T.
, , is input to the base of T. The input signal at this time changes in accordance with the pattern of the linear scale 4, is proportional to the magnitude of the command voltage E, and is proportional to the magnitude of the command voltage E'
It is a bipolar signal voltage with a polarity corresponding to the polarity of . Therefore, the current amplified by T, , T and flowing through the armature coil 31 also corresponds to this. Therefore, the pattern of the linear scale 4 is shown in Figure 1O (c
), the voltage applied to LED E and El will be the command voltage E from the servo control circuit that defines the required thrust value. Also, electronic switch IC,
Since the command voltage E' applied to the armature coil determines the direction of the thrust, an armature coil drive current having the required thrust value and thrust direction and with extremely small thrust fluctuations can be obtained.

Although FIG. 4 shows the armature coil 31, the same applies to the armature coil 32, and the LED is arranged inside the light receiving/emitting element case 62.

Electric signals obtained by a photodiode (both not shown) and the linear scale 4 are similarly amplified to become a drive current for the armature coil 32.

Incidentally, in this embodiment, it is desirable that the light-receiving surface of the light-receiving element has a slit shape as narrow as possible with respect to the moving direction of the linear scale, that is, the length direction of the dashed-dotted line in FIG.

That is, it is desirable that the width W of the light receiving surface shown in FIG. 3 is as small as possible. This is necessary in order to reproduce the pattern of the linear scale light shielding pattern 41A or 41B as a change in light amount as accurately as possible. In this example, the magnetization pitch T of the field permanent magnet is 15 m.
m, and the light-receiving width W of the photodiode was set to 1 mm, but according to a computer simulation, in this case, the difference between the light-shielding pattern waveform and the photodiode's covert pattern waveform is 1 mm.
．． It has been found that there is no problem at all since it is only 5% and the slope of the waveform pattern does not become steep.

In this embodiment, a photodiode with a light receiving width of 1 mm was used, but it goes without saying that even a photodiode with a wide light receiving width can achieve the required accuracy if used in combination with a slit.

Furthermore, in this embodiment, two sets of light receiving and emitting elements are used to obtain bipolar output signals, but even with one set of light receiving and emitting elements, it is not possible to obtain bipolar output signals with the desired pattern waveform. It is possible. However, the configuration of this embodiment is more advantageous in order to eliminate problems caused by temperature characteristics, drift, etc. of the light receiving/emitting elements.

(Example 2) FIG. 5 is a diagram showing another embodiment of the present invention.

The mechanical structure is exactly the same as that of the first embodiment, as shown in Figures 1 to 3, but it is designed to stabilize the amount of light emitted by the LED and simplify the light receiving circuit. . In the figure, E, , E are LEDs arranged inside the light receiving/emitting element case 61, R,, R are photodiodes arranged inside the light receiving/emitting element case 61, ○P, ~OP are operational amplifiers, IC, is a double-pole double-throw (DPDT) electronic switch that switches the circuit according to an external command voltage, T,
31 is a current amplification transistor, and 31 is an armature coil.

The light emitted from E, , E is blocked by the light blocking portion of the linear scale 4 according to a preset pattern, and enters R, , R□ through paths indicated by dotted lines, respectively. As in the case of FIG. 4, the emitted light has an intensity proportional to the command voltage E from the servo control circuit. However, in this embodiment, in order to stabilize the amount of light emitted by the LED, an LED E and a photodiode R1 are added, and E and R3 are separated by an appropriate distance (not shown in the figure). They are arranged so that the light emitted from E is incident on R1 and becomes a current output.

The operation of this circuit is as follows. The output voltage appears at the operational amplifier OP according to the command voltage E, and E, , E, , E
, and each LED emits light. Originally, the amount of emitted light is proportional to E, and if E is constant, it should be a constant value corresponding to E, but it varies slightly due to the influence of temperature. When the temperature is high, the amount of light increases for the same value of E. If the amount of light increases beyond a desired constant value, the amount of light incident from E and entering R3 will also increase, so the current in R3 will increase. As a result, the voltage at the negative terminal of OPo decreases, so the voltage at the output terminal also decreases, and therefore EIIE! The current flowing through the IE is reduced, which operates to reduce the amount of light from the LED. In this manner, in the circuit shown in FIG. 5, a negative feedback section for stabilizing the emitted light is added to the output circuit section.

The circuit on the incident side in FIG. 5 is configured so that the unbalanced amount of light incident on R and R3 becomes the output of the operational amplifier OP. That is, when the amount of light incident on R8 is greater, a negative signal is output, and when the amount of light incident on R1 is greater, a bipolar signal is output. This signal is amplified by the operational amplifier OP and the transistors T and T8, and becomes a current output that drives the armature coil 31. An electronic switch IC is placed in the middle, and the operation of this switch causes the OP, and T,
, TI amplifier circuits can be switched to either inverting or non-inverting type. Therefore, the command voltage E'
Accordingly, the polarity of the current flowing through the armature coil 31 can be selected.

With such a configuration, the circuit of FIG. 5 can provide the necessary thrust value and thrust direction and obtain an armature drive current that reduces thrust fluctuations, as in the case of FIG. 4.

〔Effect of the invention〕

As described above, according to the present invention, the drive current flowing through the armature coil can be controlled in a pattern that reduces thrust fluctuations, and the DC linear brushless motor has good controllability with small thrust ripples. can be obtained. The thrust ripple can be reduced without increasing the number of phases, and this is particularly effective when the number of phases is small.

In addition, the armature coil current can be freely set so that the thrust fluctuation per armature coil becomes an ideal sine wave pattern, so it can also be used for iron core type linear brushless motors. Great effect. Furthermore, after actually measuring the thrust fluctuation of the actual product, it can be corrected by changing the pattern of the linear scale 4 to reduce it to the desired degree, which can have a great practical effect. .

Further, according to the present invention, the receiving/transmitting element 61 or 62 is placed at an appropriate position relative to the corresponding coil 31 or 32 with respect to the traveling direction, for example, the coil 31 or 32.
center M (center fi perpendicular to the moving direction of the mover substrate 2)
In this case, if the light-shielding pattern on the linear scale 4 is placed at a position commensurate with this,
There is no problem in switching the current of the armature coil. In some cases, the thrust can be increased by doing this,
This is an incidental effect.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the components of an embodiment of the present invention;
The figure is a side view showing the relationship of each component in the assembled state of this embodiment, FIG. 3 is a diagram showing the light shielding pattern of the linear scale 4 in this embodiment, and FIG. 4 is a diagram showing one configuration example of the drive circuit. 5 is a diagram showing another configuration example of the drive circuit, FIG. 6 is a diagram showing a configuration example of a conventional movable armature three-phase brushless motor, and FIG. 7 is the configuration example of FIG. 6. Figure 8 is a diagram showing the principle configuration of a moving armature linear motor focusing on only one armature coil.
Figure 9 is an example of actual measurement of magnetic flux distribution by a field permanent magnet.
Figure (a) is the actual magnetic field distribution pattern, Figure 10 (b)
Figure 10(C) shows the ideal thrust waveform pattern as shown in Figure 10(b) under the magnetic field distribution pattern as shown in Figure 10(a). FIG. 4 is a diagram showing the drive current patterns required for generating a cover turn, which are determined by focusing on one armature coil, and are made dimensionless for one wavelength of magnetization pitch. 1: Stator base; 2: Mover board, 3, 31, 32.33
: Armature coil; 41, 42, 43: Hall element; 50
: Stator yoke; 51-58: Field permanent magnet; 61, 6
2: Receiving/emitting element case; 70: Stator yoke; 71-7
8: Field permanent magnet; E,, E,: LED, R
,,R,: photodiode; OP, ~OP,: obeamp; IC,: electronic switch; T+ + Tz' transistor for current amplification. ■ 4Ii Figure (a) ζn Figure 9 Figure 6 (b) Figure φVcc Figure 10 (a) (b) (C)

Claims (2)

[Claims] (1) A field permanent magnet whose N and S poles are alternately magnetized and whose magnetization pitch is T, and a field permanent magnet whose opening angle is T (N is 1 or more). (integer) system, one of which is the stator and the other is the mover, and by passing current through the armature coil appropriately according to the relative position of the mover and stator. A linear brushless DC motor configured to generate thrust in a movable element to move the movable element, characterized in that a light emitting element and a light receiving element are used as sensors for detecting the position of the movable element to detect a pattern on a linear scale. Linear brushless DC motor. (2) The light intensity of the light emitting element is changed by a control command voltage to perform thrust control.
The linear brushless DC motor according to claim 1.